The present invention relates to pole face slot fillers which are installed in slots formed in the pole faces of generator rotors.
The outer surface of a generator rotor is generally divided, in the circumferential direction, between winding regions and pole regions. Each winding region is provided with a plurality of axially extending slots, separated by teeth, the slots containing conductors which are connected at their ends to form the rotor winding.
Because of the presence of slots in the winding regions, the effective density of the rotor is greater in the pole regions than in the winding regions, causing the rotor to have different stiffness, i.e., different moments of inertia about various axes perpendicular to the axis of rotation, which leads to double frequency vibrations. Moreover, because of the above-described circumferential density variation, the rotor will tend to be deformed into an elliptical shape due to centrifugal forces.
In order to minimize these effects, it is known to provide the pole regions of such a rotor with slots generally similar to those provided in the winding regions. When this done, the pole region slots must be provided with slot fillers of a material suitable to provide the necessary magnetic flux paths in each pole region. The pole face slot fillers are held in place by wedges, which can be similar to the wedges used to retain the conductors installed in the winding region slots.
Since the pole face slot fillers increase the effective density of the pole regions, causing the rotor to have different stiffness, or different moments of inertia about various axes, these fillers are usually given a relatively short axial length so as not to affect stiffness and each pole face slot is usually provided with a plurality of such fillers, spaced apart in the axial direction of the rotor, and each pole face slot filler is generally provided with a cutout which can additionally serve as a vent passage for a radially ventilated rotor.
Because such pole face slot fillers have relatively short lengths, they have a tendency to rattle, thereby producing undesired vibrations. In addition, the pole face slot fillers tend to migrate axially when the generator is started up or stopped.